1. Field of the Invention
The present invention relates to an IC card writing system for writing data in an IC card incorporating a memory.
2. Description of the Related Art
Memories for incorporation in IC cards and of the type which output a memory identification signal to inform a user of the name of the manufacturer of the memory or the type thereof are known. Such memory identification signals enable a writing device to set program conditions suited to the memory. In general, a memory identification signal is output from a memory by the application of a predetermined high voltage to an input line of the memory.
FIG. 1 schematically shows a known IC card writing system. In FIG. 1, an IC card A incorporates a memory 1 for storing data. A writing device B is connected to an input terminal 3 and an output terminal 4 of the IC card A.
The thus-arranged IC card writing system will be operated in the manner described below. After the system has been turned on, the writing device B applies a high voltage which may be about 12 V to the input terminal 3 of the IC card 1, so as to obtain a memory identification signal as a result of the high voltage being applied to the memory 1. The voltage is, for example, applied to a ninth address line A.sub.9 in case of using a M5M27C256-type IC for the memory 1. The memory 1, to which a high voltage and the other required voltages have been applied, outputs an identification signal, for example, 8-bits in length, from the output terminal 4 of the IC card A to writing device B through a data bus. The writing device B, where the identification signal is detected, then begins to write data in the memory 1 in a suitable form.
The IC card A illustrated in FIG. 1, however, is only theoretical and, in general, practical IC cards incorporate a peripheral IC 2 or a widely used IC gate such as a buffer circuit connected between the memory 1 and the input terminal 3 as shown in FIG. 2, so as to prevent noise due to static electricity. For example, a 74HC245-type can be used as the peripheral IC 2.
In FIG. 2, the IC card A has resistance to static electricity by virtue of the peripheral IC 2. This IC card A incorporating the memory 1 and the peripheral IC 2 can withstand several thousand volts of static electricity while an IC card incorporating only the memory 1 can withstand only several hundred volts of static electricity. In addition, in a case where a plurality of memories 1 are incorporated in one IC card A and a plurality of connection signals are input to and output from the memories in parallel, peripheral IC 2 prevents a delay waveform from being generated between the connection signals. In this manner, the peripheral IC 2 is a necessity for an IC card having a large capacity.
Suitable elements that may be utilized in an IC card A as the memory 1 include a PROM (a programmable read only memory). Suitable PROMs in turn include an EPROM (an erasable programmable read only memory) into which data can be electrically written and from which data can be erased by ultraviolet radiation, and an EEPROM (an electrically erasable programmable read only memory) from which data can be electrically erased. There has recently been an increasing demand for reductions in the level of power consumption of IC cards, and lower voltages have been adopted accordingly for writing data in EPROMs.
However, in a case where the peripheral IC 2 is incorporated in the IC card A between the input terminal 3 and the memory 1 for generating an identification signal by the receipt of a high voltage as shown in FIG. 2, the high voltage is applied by the writing device B to the memory 1 through the peripheral IC 2. Generally, the voltage applied by the writing device B to obtain an identification signal is about 12 V. Combined with the fact that the maximum rated voltage for an IC is in general about 7 V, this is rather high, and may lead to some risk of the peripheral IC 2 being damaged.